Field of the Disclosure
Embodiments disclosed herein relate to systems and methods for strengthening wellbores during drilling. More specifically, embodiments disclosed herein relate to systems and methods using a probabilistic approach for strengthening wellbores. More specifically still, embodiments disclosed herein relate to systems and methods using probabilistic approaches based on Monte Carlo for simulating and determining options during wellbore-strengthening operations.
Background Art
Lost circulation is a recurring drilling problem, characterized by loss of drilling mud into downhole formations that are fractured, highly permeable, porous, cavernous, or vugular. These earth formations can include shale, sands, gravel, shell beds, reef deposits, limestone, dolomite, and chalk, among others. Other problems encountered while drilling and producing oil and gas wells include stuck pipe, hole collapse, loss of well control, resulting in loss of or decreased production.
Induced mud losses may also occur when the mud weight, required for well control and to maintain a stable wellbore, exceeds the fracture resistance of the formations. A particularly challenging situation arises in depleted reservoirs, in which the reduction in pore pressure weakens the effective strength of the hydrocarbon-bearing rocks, but neighboring or inter-bedded low permeability rocks, such as shales, maintain their pore pressure. This can make the drilling of certain depleted zones difficult or impossible because the mud weight required to support the shale exceeds the reduced fracture resistance of the depleted formations.
Currently, several wellbore-strengthening methods are used to reduce the incidence of lost circulation during drilling. Wellbore strengthening refers to creating and filling small fractures with loss-prevention materials (LPM) to alter the near-wellbore hoop stress, thereby increasing the fracture resistance above the in-situ minimum horizontal stress. One such technique is plugging an existing or drilling-induced fracture at the fracture tip. Another method may include plugging a fracture at the wellbore wall, also known in the art as “stress-cage.”
Methods of modeling lost circulation, and thus methods of modeling and formulating mechanisms to prevent or stop lost circulation typically use a deterministic approach. More specifically, for a given set of inputs, there is only one possible result from the fracturing/lost circulation simulation. For example, modeling the formation may provide information about whether a given lost circulation solution will effectively prevent lost circulation. Current methods of determining whether particular solutions effectively prevent lost circulation are limited by the number of variables and formation properties that may be considered.
Accordingly, there exists a need for systems and methods of more effectively modeling lost circulation loss and developing solutions for lost circulation during drilling.